Optimism aside, US struggles to meet goals in Afghanistan

"The bottom line is, in key areas of the country, the security situation is still very fragile, and in some places there is risk of deterioration," Obama said Thursday in announcing what he called a calculated adjustment to his plan.

Others question whether keeping nearly 10,000 U.S. troops there in 2016 and then holding at 5,500 troops beyond that will make a significant difference, given the uneven results from 14 years of efforts to build and professionalize an Afghan army and police force paid for largely by the United States.

Just days ago the top U.S. commander in Afghanistan, Gen. John Campbell, told a congressional committee that Afghan forces are unable to fight without U.S. support, that "we have just started" creating an Afghan air force, and that "it will take time" to develop competent Afghan battle commanders.

Year after year, in public statements and periodic updates to Congress, Pentagon officials have insisted the Afghan army and police were getting better, suggesting success was just around the corner if Americans would remain patient.

Last fall a senior U.S. commander said Afghan troops were dying at a rate that was "not sustainable," and the combat losses have only accelerated this year, according to the Pentagon's latest report to Congress.

Stephen Biddle, a George Washington University professor of political science who periodically advises American commanders, says the problem with the U.S. approach is that it has focused too narrowly on filling the Afghan forces' obvious gaps in soldiers, weapons, equipment and training.